A traction drive usually comprises an endless traction element, such as a belt or chain, and at least two pulleys of which one can function as an input and the other one as an output. Such traction drives can be used for example in connection with internal combustion engines of a motor vehicle for driving auxiliary apparatuses or accessories, wherein a first pulley is positioned on the crankshaft of the internal combustion engine and drives the belt.
Further, belt pulleys are associated with the auxiliary apparatuses, such as a water pump, a generator or an air conditioning compressor, and are rotatingly driven by the traction drive. In conventional traction drives the auxiliary apparatuses are designed as consumers, i.e., they are driven by the pulley of the crankshaft via the belt. A slack side of the belt is formed between the crankshaft and the apparatus adjoining the crankshaft in the direction of the circulation of the belt, said adjoining apparatus typically being a generator. In order to ensure that the traction member is sufficiently wrapped around the drive pulley, the traction member is pretensioned by a tensioning roller of the tensioning device.
From EP 1 277 989 A2 a belt tensioning device is known with a housing and a roller carrier pivotably connected to the housing. The roller carrier is radially and axially supported relative to the housing by means of a bearing and is pretensioned relative thereto by a tension-loaded helical spring. The roller carrier is thus axially fixed to the housing via the bearing and the helical spring. A damping device is provided which dampens relative movements between the roller carrier and the housing in such a way that the damping effect is greater at an increasing tensioning force than at a decreasing tensioning force. The damping device comprises a damping bush and a band spring which, at its first end, is rotationally fixed at the housing or at the roller carrier and, at its second end, it is rotationally fixed at the damping bush.
DE 196 03 558 C2 proposes a belt tensioning device with a receiving housing, with a roller carrier pivotably connected thereto, as well as a bearing and damping device. The bearing and damping device comprises a bearing and damping cone which is pretensioned in respect of tension and torsion by a helical spring.
From EP 0 858 563 B1 a tensioning device is known for a traction element, which tensioning device comprises a housing and a tensioning arm which is rotatably supported relative to the housing by a friction bearing. The friction bearing faces of the friction bearing are provided in the form of conical faces arranged parallel relative to one another and concentrically relative to the tensioning arm axis. A helical rotational spring is supported between a support at the tensioning arm and a support at the housing, wherein in the mounted condition, a torsion pretension and an axial pretension is applied by said spring. Thereby, an axial force of the helical rotational spring is introduced into the friction bearing as a reaction force effective perpendicularly relative to the friction bearing faces, so that the friction bearing faces are pressed against one another under the axial force.
Tensioning devices with cylindrical damping systems are relatively complex and therefore expensive in respect of production and assembly. Tensioning devices with conical damping systems are more susceptible in respect of an undesirable tilt of the tensioning arm relative to the housing.